The objectives of the research are to understand the primary actions of narcotic analgesics on single neurons and the way in which these alter during the development of tolerance and physical dependence. The role of enkephalin as it affects single neurons will also be investigated. Three peripheral mammalian tissues will be used. Experiments will be conducted by single cell recording in vitro from the myenteric plexus of the guinea-pig ileum, the vas deferens of the mouse and the nodose ganglion of the rat and guinea-pig. The properties of single myenteric neurons will be determined by intracelluar recording; the mechanism of action of enkephalin on the membrane properties will be examined, with particular emphasis on the role of calcium and other ions on this action. Neurons will be made tolerant to and dependent on opiates by in vitro incubation: the factors which influence the development of these changes will be investigated. The release of neurotransmitter in the vas deferens of the mouse will be studied by recording excitatory junction potential amplitudes from single smooth muscle cells. The factors which affect the ability of opiates to depress transmitter release will be studied; these include calcium ions, cyclic nucleotides and pretreatment of the tissue with opiates both in vivo and in vitro. Single neurons in the nodose ganglion and the C-fibers of the vagus nerve will be studed with respect to the acute and chronic effects of opiates and enkephalin. Both intracellular recording and extracellular sucrose-gap recording will be used. The results are expected to elucidate the way in which enkephalin and narcotic analgesics act on single neurons in both naive and drug-dependent animals. The experiments will help to distinguish between the primary and secondary changes which occur in single neurons during chronic exposure to opiates.